1. Field of the Invention
This invention relates to a composition for electrical applications based on an ethylene polymer containing a talc filler coated with a metallic salt of a fatty acid having 8-20 carbon atoms.
2. Description of the Prior Art
Compositions which are employed on electrical wire and cable are, in many cases, prepared from compositions which are based on vulcanizable, or crosslinkable, ethylene polymers. These ethylene polymer based compositions may be filled with various fillers, as well as coated fillers, as described, for example, in U.S. Pat. Nos. 3,148,169, 3,832,326 and 3,922,422.
The fillers, when added to ethylene based polymer compositions, reduce the cost of the composition as well as increase the mechanical properties of the compositions, in that they toughen the materials as for example, increasing the abrasion resistance. Additionally, the fillers decrease the flammability of the ethylene polymer by their addition thereto.
However, there are certain adverse effects in the use of filled ethylene polymer based compositions. The problems encountered in the use of fillers include the fact that the insulation properties, for example, are more susceptible to moisture, i.e., the insulation on a finished wire or cable is more susceptible to moisture.
Additionally, the elongation is generally adversely affected by the use of a filler. Also, in order to process the ethylene based compositions so as to adapt them to be placed, as, for example, insulation, on the electrical conductor components of the wire and cable, it is usually necessary to admix the components of the compositions at high temperatures, and to extrude them, again at high temperatures, onto the electrical conductor. When certain fillers are used in combination with certain types of ethylene polymers or in certain types of ethylene polymer based compositions, the entire curable composition is susceptible to scorching during the high temperature processing thereof prior to the vulcanization of the composition on the electrical conductor. Scorching is, in effect, the premature vulcanization of the insulation composition. This premature vulcanization usually occurs, when it occurs, in the barrel or die head of the extruder in which the insulation composition is being processed, at elevated temperatures, prior to its being extruded onto an electrical conductor, and prior to its intended vulcanization. When an insulation composition is scorched in the extruder, the extruded composition will have imperfections in the form of discontinuity and roughness in the surface of the extrudate, and lumps or surface ripples caused by gel particles in the body of the extrudate. In addition, excessive scorching may cause enough of a pressure build-up in the extrusion device to require a cessation of the extrusion operation entirely.
Talc itself is a poor filler, since the tensile and elongation properties of a talc filled ethylene polymer based composition are unacceptable. These unacceptable properties of tensile strength and elongation indicate incompatibility between the talc and ethylene polymer.